In an electrophotographic imaging process performed by an electrostatic imaging apparatus an imaging substance (typically a dry toner) is transferred (either directly or indirectly) from an optical photoconductor to a sheet of imaging media by an electrostatic process. Examples of electrostatic imaging apparatus include printers, photocopiers, facsimile machines, and xe2x80x9cmulti-functionxe2x80x9d imaging apparatus which perform two or more of the afore-mentioned imaging processes. Such imaging apparatus are commonly known as xe2x80x9claser printersxe2x80x9d, since an electrostatic image is formed on the optical photoconductor through the use of a selectively pulsed laser. Imaging media used in such electrostatic imaging apparatus can include, for example, sheets of paper, transparencies, envelopes, and card stock. After the imaging substance has been transferred to the imaging media the imaging substance is fixed to the imaging media by a fusing process, which typically includes passing the imaging media between two rollers which are part of a fuser. The fusing rollers apply heat and/or pressure to the imaging media to fix the imaging substance to the imaging media.
The fuser typically includes two parallel, adjacent, fuser rollers, though which the imaging media is passed during the fusing process. Parameters which affect the fusing process include the pressure between the fuser rollers (which is subsequently applied to the imaging media), the heat input to one or both of the fuser rollers, and the rate at which the imaging media is passed through the fuser rollers. Ideally, these parameters are selected to optimize the fusing process. Optimization of the fusing process includes providing sufficient energy to fuse the imaging substance to the imaging media without deteriorating the quality of the formed image or deleteriously affecting the quality of the imaging media. For example, if insufficient heat and/or pressure is applied during the fusing process, then the imaging substance can have a tendency to afterwards separate from the imaging media. Further, if excessive heat and/or pressure is applied during the fusing process, then the imaging media can exhibit excessive curling, and/or the imaging substance will xe2x80x9crunxe2x80x9d (i.e., spread beyond the intended locations of application) on the imaging media.
The results of the fusing process can be affected by the types and/or conditions of the imaging media. More specifically, at least the thickness, the width, the moisture content, and the material of construction of imaging media can affect the results of the fusing process. For example, if a given fusing process is applied to a first sheet of imaging media having a first thickness, and the same process is thereafter applied to a second sheet of imaging media having a second thickness which is different than the first thickness, then the fusing process can be compromised with respect to at least either the first or the second sheet.
Accordingly, it is desirable that a fusing process in an electrophotographic imaging apparatus be adjustable to accommodate variances in the imaging media to be processed by the fusing process. In this way the quality of the resultant image generated on the imaging media can be enhanced. Further, deleterious affects to the imaging media itself can also be reduced.
In one non-limiting embodiment an apparatus for controlling a fuser in an imaging apparatus includes a first fuser roller and a second fuser roller in parallel, adjacent orientation and configured to receive sheet media therebetween. The apparatus further includes an electrical voltage source applied across the fuser rollers. The apparatus also includes a voltage difference measuring device configured to measure a difference in the electrical voltage across the first and second fuser rollers when sheet media is received between the first and second fuser rollers, and to generate a voltage difference signal in response thereto. The device includes a controller which is configured to receive the voltage difference signal and to generate a fuser parameter control signal in response thereto. The apparatus also includes a fuser control device responsive to the fuser parameter control signal.
In another embodiment a method of determining characteristics of sheet media includes providing first and second electrically conductive rollers in parallel contact, and applying a preselected voltage across the first and second rollers. Sheet media is then placed between the first and second rollers, and the voltage difference across the first and second rollers is measured. The measured voltage difference is then used to determine characteristics of the sheet media.
These and other aspects and embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein: